ATLANTA -- It's unclear just how long Danny Espinosa has been dealing with pain in his left shoulder, or what effect it's had on his performance.

But this much is certain: Something about Espinosa wasn't right over the weekend, and now there's a chance something is seriously wrong with the shoulder.

Nationals manager Davey Johnson said the second baseman finally informed coaches of the problem late during last night's 5-1 loss to the Braves, essentially asking out before his final at-bat in the top of the ninth. Thus ended a brutal series for Espinosa, one in which he went 0-for-11 with nine strikeouts and a groundball double play.

Espinosa had been swinging a red-hot bat for a while. Over a 21-game stretch from Aug. 13-Sept. 5, he hit .333 with five homers, 11 RBI and a .947 OPS. But he's now 4 for his last 34, with only two RBI and 16 strikeouts.

How much of that is direct result of the shoulder? There's no way to know, but certainly it would seem to have had some effect.

Of more concern might be the manner in which Espinosa finally asked out of last night's game. This from a guy Johnson calls his "Iron Man," one who gets furious anytime he's not in the lineup.

Johnson also said Espinosa was asking teammate Adam LaRoche about how the first baseman's shoulder felt early last year (when LaRoche had a torn labrum that destroyed his season).

There's a red flag right there.

"I'm very concerned about him," Johnson said.

We can only wait and see what today's MRI shows -- Espinosa is scheduled to be examined by team orthopedist Wiemi Douoguih at 1 p.m. -- but Johnson already doesn't expect to have him for this week's series against the Dodgers.

And what if Espinosa needs to miss more time than that, or perhaps is even done for the season?

The Nationals are well-positioned to deal with such a blow, thanks to the presence of Steve Lombardozzi, who has capably filled in both left field and second base for prolonged stretches this season when Michael Morse and Ian Desmond spent time on the disabled list.

Lombardozzi would give the Nationals good at-bats and play solid, if not spectacular, defense. But let's be honest: His best is not nearly as good as Espinosa's best. When Espinosa is on top of his game, he's a major power threat at the plate and a Gold Glover in the field.

He hasn't, of course, been much of a threat at the plate over the last week. And now it appears we know why.

There are only two questions remaining: What exactly is going on in Espinosa's shoulder, and what will the Nationals need to do about it?